[GHC] #12782: Type inference shows (Num (a -> a), Num a)

[GHC]

#12782: Type inference shows (Num (a -> a), Num a)
-------------------------------------+-------------------------------------
           Reporter:  ciupakabra     |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
  (Type checker)                     |
           Keywords:                 |  Operating System:  Linux
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Defining f and g as:
 > f x = x + 1
 > g x y = x + y

 Entering
 :t f . g
 gives:
 f . g :: (Num (a -> a), Num a) => a -> a -> a

 Formally, it is correct, since Num (a -> a) is never going to be a number.
 Though me and my tutor thought it might be a bug, and f . g shouldn't be
 recognised as a well-formed expression.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12782>
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